Abstract Plasmodium vivax blood stage malaria infections are still mostly treated with chloroquine although there are replacement medicines available that provide symptomatic relief. On the other hand, primaquine, is the only licensed drug that will give a radical cure of P. vivax malaria and clear hypnozoites, the latent liver states responsible for relapses as well as transmission in temperate zones where the mosquito vector may not be present year round. It remains one of the most important and yet enigmatic drugs in the antimalarial arsenal. Although primaquine resistance has been documented it is difficult to quantify how much of the P. vivax disease burden is due to drug resistance because there are no molecular markers than can indicate parasite sensitivity to primaquine, nor established methods for measuring resistance. The aim of this proposal is to exhaustively study how resistance to primaquine may emerge in a laboratory setting using rodent models of malaria. I will develop methods for identifying single base changes in evolved drug resistant lines of Plasmodium berghei, a rodent model of human malaria. I will then examine the complete constellation of genetic changes that emerge when mice infected with P. berghei are exposed to sublethal drug concentrations. Loci that are implicated in resistance will be confirmed through allelic exchange, complementation or genetic crosses. The proposed studies will accelerate malaria parasite resistance studies in the following ways. First I will create tools that can be used to study drug resistance and host immune evasion mechanism in P. berghei, Second, I will identify one or more candidate genes or alleles whose association with primaquine resistance in P. vivax can be tested in field studies. Thirdly, I will enhance our global understanding of how eukaryotic pathogens become resistant to drugs at the single base level following physiologically relevant drug selection.